-LRB- CNN -RRB- -- Firefighters gained ground in recent days in the battle with a wildfire that burned 84 buildings and blackened 28,000 acres of dense forest in northern California .

The Ponderosa fire , which is in a remote area of Shasta County , California , is just one of 42,750 wildfires that have burned 6,901,035 acres in the United States this year , according to the National Interagency Fire Center .

The fire , ignited by lightning five days ago , was 57 % contained by Thursday , allowing some families forced from their homes to return , fire officials said .

The Ponderosa fire still threatens 900 homes , forcing those residents to evacuate . Nearly 2,500 people , equipped with 263 firetrucks and 11 helicopters , are involved in the effort to stop the Ponderosa fire .

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Shasta is one of three northern California counties for which Gov. Jerry Brown has declared states of emergency because of wildfires this week . The other counties included in the declaration , which makes emergency funding available to fight the blazes , are Plumas and Tehama .

In Plumas County , the Chips fire has burned 63,147 acres , most of it in the Plumas National Forest . The 1,146 personnel fighting it have managed to gain 40 % containment , according to officials .

`` Today 's mission is clear : hold , hold , hold , '' Operations Section Chief Rob Laeng told firefighters at their morning briefing Thursday .

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In Tehama County , the battle is almost over against the Mill fire . It is 95 % contained after 1,680 acres burned , according to the California Department of Forestry and Fire Protection .

A fire that has burned nearly 100,000 acres , mostly managed by the U.S. Forestry Service , in northern Idaho is still just 5 % contained three weeks after it began , officials said . The Trinity Ridge fire threatens the community of Featherville , but efforts to create a buffer for the area have been `` very successful , '' according to a statement on the fire 's incident website .

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California 's Ponderosa Fire burns 84 buildings and threatens 900 homes

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Gov. Jerry Brown declares states of emergency in 3 California counties because of wildfires

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`` Today 's mission is clear : hold , hold , hold , '' chief tells firefighters battling California 's Chips Fire

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42,750 wildfires have burned 6,901,035 acres in the United States this year , fire center says